The present invention relates to an electronic frequency tuning magnetron which oscillates microwaves. More particularly, the present invention relates to a constitution of a magnetron for changing oscillating frequency by external electric signals with a simple configuration.
FIG. 11 shows a basic configuration of a conventional magnetron. In the magnetron, a cathode 1 is provided at the center and an anode shell 2 is concentrically provided outside the cathode 1. A plurality of anode vanes 3 is provided to divide the inner space in a circumferential direction. In other words, the anode vane 3 serves as a positive electrode relative to the cathode 1 and a resonator for determining an oscillating frequency at the same time. Thus, the anode vanes 3 form the resonant cavity with the inner wall of the anode shell 2.
In order to best stabilize the n-mode oscillation of the magnetron, line-shaped conductors called strap 4 in contact with alternate ones of the vanes 3 serving as partitions of the resonant cavity which is segmented into a plurality of spaces as mentioned above. In the magnetron with such configuration, an oscillating frequency is determined by reactance which is configured by both the straps 4 and the segment cavity.
As mentioned above, an oscillating frequency is determined by mechanical configuration in the configuration of the magnetron as shown in FIG. 11. Thus, the oscillating frequency cannot be changed if the reactance which is determined by mechanical configuration is not changed. As a typical practicable frequency tuning means, there is a means configured on the basis of the principle described in p. 562 of “MICROWAVE MAGNETRON”, MIT Radiation Laboratory Series. According to the means, frequency can be changed by modifying the reactance of the resonant cavity by inserting a metal into the resonant cavity. In other words, the insertion of the metal into the resonant cavity leads to the increase of the inductance of the resonant cavity. In particular, when the metal is inserted in the vicinity of the front edge of the anode vane 3 serving as a partition of the resonant cavity, the capacitance increases and the oscillating frequency becomes higher as a result.
Besides the above-mentioned resonant cavity, as a means for mechanical modulation, a method in which a metal is advanced to the strap 4 or anode vane 3 is described in p. 569 to 572 of “MICROWAVE MAGNETRON”, MIT Radiation Laboratory Series.
Moreover, as described in Japanese Unexamined Patent Publication No. 100066/2006, oscillating frequency can be controlled by providing an external resonant cavity (or external space) at the outside of a tube via a hole (or slit) and adjusting the position of a metal plate (or movable metal piece) provided in the external resonant cavity by mechanically shifting the plate to change the reactance of the resonant cavity from the outside of the tube.